<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div id="app">
        {{msg}}
        <button @click="a">+</button>
        <button @click="b">-</button>
    </div>
</body>
<script src="../js/vue.js"></script>
<script>
    const app = new Vue({
        el:'#app',
        data: {
            msg:0
        },
        methods: {
            a(){
                this.msg++
            },
            b(){
                this.msg--
            }
        }
    })
</script>
</html>